The use of printed circuitry in which electronic components are formed on one or more surfaces of an insulating board is an established procedure in the electronics industry. For reasons of compactness, performance and appropriate interconnection between various components, multi-layer circuit board arrangements have been developed in which electrical components on one layer are interconnected with other components on a remote surface of another layer. An example of a multi-layer circuit board is disclosed in Dahlgren et al., U.S. Pat. No. 3,499,218. Interconnections between remote layer surfaces may be effected by means of plated through holes. That is to say, a hole is drilled through the circuit board layer between the circuit components to be connected and the interior of the hole is plated with a conductive material to establish a conductive path between the surfaces of the layer.
In the past, it has been attempted to mechanically and electrically connect the layers of a multi-layer circuit board to each other by soldering. Difficulties have been encountered, however, as a result of excessive solder flow which penetrates beyond the intended joint areas. Excessive solder flow may interfere with adhesive bonds established between nonelectrically conductive areas of adjacent layers and also may cause short circuits between different circuit elements of the printed circuitry. Accordingly, there is a need for improved bonding techniques which can establish an electrically and mechanically sound bond between adjacent layers of a multi-layer circuit board without any flow of conductive material beyond the desired conductive joint area.
Thermal compression bonding techniques are known in contexts unrelated to the present invention. For example, thermal compression bonding of dissimilar metals under vacuum is disclosed in Clarke, U.S. Pat. No. 3,619,896. Use of such techniques is unknown, however, to create a bond and electrically conductive path between two identical metals through one or more layers of non-conducting circuit board material in a multi-layer circuit board.